R.T.N.

My understanding of RTN is that it's not a tissue peeling issue - it's a tissue mortality and bleaching white issue. I am not too familiar with this condition, but it might be helpful to look at what changes have occurred in the tank lately, like within the last month or two. Also think about chemical warfare that goes on between coral. How long have you had these pieces and was there any dead or peeling tissue when you got them. How long has your tank been set up? Hows it's bilogical filtration. Is the skimmer working properly. A skimmer is almost essential for acropora, in my opinion. Anything else die lately?

Mark

RTN, rapid tissue degeneration, or rapid tissue necrosis as they are referred to can be toxic to all of the acros, or even other sps corals in your tank.  The book Aquarium Corals by Borneman has a section on this (p.381-384).  The recommendation provided there is as follows "If RTN is detected in any specimen in the display aquarium, it should be removed from the tank as soon as possible to avoid triggering further RTN reactions in healthy corals. . . then the coral branches may be broken off, or fragmented, well ahead of the area where tissue loss has begun.  The healthy-looking fragments should be removed to a quarantine facility for at least several days before being returned to the tank.  The remainder of the affected coral should be discarded entirely.  RTN is almost invariably fatal, and its presence should be acted on quickly.  It is one of the few times where fast action is required by the aquarist to prevent the loss of one or many corals."  Some people also report success with Lugol's dips.  The cause is almost always due to a stress that the coral has gone through; ie., shipping, acclimation, placement in the tank.  During shipping, many corals secrete a lot of mucous.  This, coupled with the fact that they are in stagnant water, can trigger RTN.  If they are not taken care of at your LFS, and quickly passed on to us, RTN may be lying in wait.  RTN can either be the result of a specific pathogen, or a result of the coral digesting its own tissue.   HTH - Jared.

I don't understand, why would acropora need to go to the bottom of the tank to acclimate? It needs lots of light and water movement so should always be placed in bright light and fast water!

Again, I recommend a skimmer.

In my experience, Acropora does not like it when there is a lot of caulerpa. That's because caulerpa adds it's own chemicals to the water.

You should look for other "non-caulerpa" algaes for your refugia, in fact if you haven't heard, caulerpa can suddenly dissolve, and in as little as 12 hours all the nutrients captured by the caulerpa are back into the aquarium water.

I think caulerpa is too salty for the house plants.

Just a warning, but within the first year of a tanks life it goes through all kinds of changes and adjustments as the biological filtration and the ecology change. Lots of stuff grows up and then dies off as other things grow and compete for their new home.

Mark